From the viewpoint of display quality deterioration of a liquid crystal display device, it is necessary to prevent a crosstalk caused by a coupling noise to a common electrode. A technology for adjusting a voltage input to the common electrode on the basis of a detected voltage at the common electrode is called Vcom feedback. For example, a first prior art is known as a configuration of Vcom feedback control in the liquid crystal display device that includes neither a touch panel nor a touch function (See Japanese Unexamined Patent Application Publication No 2008-304806).
Nowadays, an electrostatic capacitance type touch panel is frequently used in a smartphone and a tablet terminal as a detection system of the touch panel. Various systems are studied as a combination system of the touch panel and a liquid crystal display panel. For example, a liquid crystal display device including the touch panel outside the liquid crystal display panel including a TFT (Thin film Transistor) substrate and a color-filter substrate is called an out cell. For example, a second prior art is known as a method for driving the Vcom feedback control in the out cell (See Japanese Unexamined Patent Application Publication No 2013-109095).
Specifically, in the second prior art, the common electrode and a liquid crystal layer are disposed between two glass substrates, and a sensor electrode for the touch panel is provided on an opposite side to the liquid crystal layer of one of the glass substrates. Because a variation in potential at the common electrode propagates to a potential at the sensor electrode, the second prior art discloses a Vcom feedback circuit that performs the feedback to the common electrode on the basis of a feedback signal input from the common electrode and a horizontal synchronizing signal in order to flatten a signal of the common electrode.